The present invention relates to a process and device for regulating the flow of fluid through plastic tubing primarily, although not exclusively, in the administration of parenteral fluids.
For administering parenteral fluids, disposable single use kits have come into use. Typically, such kits include a length of flexible synthetic plastic tubing and a flow regulating device attached to the tubing for adjusting the delivery of the gravity flow of the parenteral fluid to the desired rate, which is typically on the order of 2 milliliters per minute.
Generally speaking, it is desired to maintain the flow rate of fluid constant with time. To this end, a variety of flow regulating devices have heretofore been devised and marketed. Generally, these comprise roller, pinch and screw clamps or the like which are adjusted to more or less constrict a given circumferential section of the synthetic plastic tubing to selectively choke the flow of the fluid therethrough. In these prior devices, the objective of maintaining a desired constant flow rate has been sought to be attained merely by devising the flow regulating device with positively acting mechanical means which are intended to maintain their adjusted position, more or less constricting the tube to attain a desired, effective, open cross-sectional area within the tube. However, the known devices apparently do not take into account the characteristic of the synthetic plastic known as "cold flow." In the prior devices, when the tubing is clamped, as a consequence of the induced strain or deformation, the plastic material apparently cold flows such that the resultant flow cross-sectional area, sometimes even a few minutes after having been subjected to the deformation, is significantly modified. A consequence of this phenomenon is that the liquid flow rate will vary even though there has been no mechanical change of the clamp configuration. As a result, the prior art devices must be constantly checked and re-adjusted because the flow will "drift" from its original settings. Furthermore, the presently used roll-clamps can be dislodged, or shifted in position by external disturbances. The consequences of this could be dangerous or disasterous since excessive flow rates may result.